Abstract

Purpose: Renal inflammation is prevalent in the chronic autoimmune disease systemic lupus erythematosus (SLE) and drives the progression of kidney injury. Inflammation in SLE results from a loss of self-tolerance and the production of autoantibodies against nuclear antigens. However, other immunoregulatory mechanisms, such as the cholinergic anti-inflammatory pathway, may also be dysregulated and contribute to aberrant systemic and renal inflammation in the disease. The cholinergic anti-inflammatory pathway is a protective, neuroimmune mechanism thought to involve neurotransmission between the parasympathetic vagus and the sympathetic splenic nerves. In order to confirm the importance of the splenic nerve in this pathway, others have used 6-hydroxydopamine (6OHDA), a neurotoxin that depletes catecholamines, to chemically denervate the spleen and thereby dampen the sympathetic component of the cholinergic anti-inflammatory pathway. We hypothesized that splenic injection of 6OHDA would further disrupt the cholinergic anti-inflammatory pathway in a mouse model of SLE and result in increased renal inflammation and worsened disease severity, which would highlight the importance of the splenic nerve in quelling renal inflammation. Methods: In the current study, female SLE and control mice were injected with 6OHDA (120 µg in 60 μl saline) or vehicle directly into the spleen at 33 weeks of age (n = 6/group). To confirm splenic denervation with 6OHDA, we utilized the glyoxylic acid condensation reaction on 12 μm spleen sections of representative animals and verified that catecholamine histofluorescence was diminished in 6OHDA-treated mice (205 vs. 111 histofluorescent foci). Results: Renal cortical TNF-α (normalized to total protein) was increased in SLE mice compared to controls (3.1e6 ± 1.2e5 vs. 7.8e5 ± 1.6e4 intensity units; p = 0.029), and 6OHDA exacerbated this pro-inflammatory cytokine in SLE mice (7.6e6 ± 2.4 intensity units; p = 0.048) with no effect in controls (2.4e6 ± 6.6e5 intensity units; p = 0.697). Anti-dsDNA autoantibodies were elevated in SLE mice compared to controls (2.1e4 ± 5.7e3 vs. 1.0e4 ± 4.7e3 activity units; p = 0.013), but 6OHDA did not alter this measure of disease severity in SLE mice (1.8e4 ± 5.2e3 activity units; p = 0.692). Albumin excretion rate (AER) was elevated in SLE mice compared to controls (160.7 ± 28.0 vs. 2.7 ± 2.7 mg/dL; p < 0.001). 6OHDA accentuated the increase in AER in SLE mice (454.2 ± 150.2 mg/dL; p = 0.010) but had no effect in controls (27.5 ± 17.0 mg/dL; p = 0.754). Conclusions: In summary, 6OHDA aggravated renal inflammation and injury in SLE mice indicated by heightened renal cortical TNF-α and AER. This suggests that chemical splenic denervation may disrupt endogenous, sympathetically-mediated anti-inflammatory mechanisms. Further studies are needed to confirm the role of the splenic nerve in regulating renal inflammation.

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Purpose: Renal inflammation is prevalent in the chronic autoimmune disease systemic lupus erythematosus (SLE) and drives the progression of kidney injury. Inflammation in SLE results from a loss of self-tolerance and the production of autoantibodies against nuclear antigens. However, other immunoregulatory mechanisms, such as the cholinergic anti-inflammatory pathway, may also be dysregulated and contribute to aberrant systemic and renal inflammation in the disease. The cholinergic anti-inflammatory pathway is a protective, neuroimmune mechanism thought to involve neurotransmission between the parasympathetic vagus and the sympathetic splenic nerves. In order to confirm the importance of the splenic nerve in this pathway, others have used 6-hydroxydopamine (6OHDA), a neurotoxin that depletes catecholamines, to chemically denervate the spleen and thereby dampen the sympathetic component of the cholinergic anti-inflammatory pathway. We hypothesized that splenic injection of 6OHDA would further disrupt the cholinergic anti-inflammatory pathway in a mouse model of SLE and result in increased renal inflammation and worsened disease severity, which would highlight the importance of the splenic nerve in quelling renal inflammation. Methods: In the current study, female SLE and control mice were injected with 6OHDA (120 µg in 60 μl saline) or vehicle directly into the spleen at 33 weeks of age (n = 6/group). To confirm splenic denervation with 6OHDA, we utilized the glyoxylic acid condensation reaction on 12 μm spleen sections of representative animals and verified that catecholamine histofluorescence was diminished in 6OHDA-treated mice (205 vs. 111 histofluorescent foci). Results: Renal cortical TNF-α (normalized to total protein) was increased in SLE mice compared to controls (3.1e6 ± 1.2e5 vs. 7.8e5 ± 1.6e4 intensity units; p = 0.029), and 6OHDA exacerbated this pro-inflammatory cytokine in SLE mice (7.6e6 ± 2.4 intensity units; p = 0.048) with no effect in controls (2.4e6 ± 6.6e5 intensity units; p = 0.697). Anti-dsDNA autoantibodies were elevated in SLE mice compared to controls (2.1e4 ± 5.7e3 vs. 1.0e4 ± 4.7e3 activity units; p = 0.013), but 6OHDA did not alter this measure of disease severity in SLE mice (1.8e4 ± 5.2e3 activity units; p = 0.692). Albumin excretion rate (AER) was elevated in SLE mice compared to controls (160.7 ± 28.0 vs. 2.7 ± 2.7 mg/dL; p < 0.001). 6OHDA accentuated the increase in AER in SLE mice (454.2 ± 150.2 mg/dL; p = 0.010) but had no effect in controls (27.5 ± 17.0 mg/dL; p = 0.754). Conclusions: In summary, 6OHDA aggravated renal inflammation and injury in SLE mice indicated by heightened renal cortical TNF-α and AER. This suggests that chemical splenic denervation may disrupt endogenous, sympathetically-mediated anti-inflammatory mechanisms. Further studies are needed to confirm the role of the splenic nerve in regulating renal inflammation.